Paging systems are now widely used to communicate information to a person carrying a mobile paging unit. Typically, the paging system includes one or more paging terminals connected together in a network. The paging terminal network may then be connected to the public switched telephone network (PSTN) or other types of networks such as the Internet so that parties may generate paging messages for transmission to the mobile paging unit. Also included in the paging system are paging transmitters that are connected to one or more paging terminals. The paging terminals formulate and format the paging messages and forward the paging messages to the paging transmitters for transmission.
The paging transmitters transmit the paging messages in accordance with predetermined paging protocols, such as POCSAG, FLEX, and ERMES. These protocols include multiple layers. For example, the second-lowest layer, the data link layer, governs direct host-to-host communication over the communications medium between the hardware at different hosts; the highest layer is used directly by user applications. Each layer builds on the layer beneath it. The advantages of different layers of protocols is that the methods of passing information from one layer to another are specified clearly as part of the set of protocols on different layers that work together (i.e., protocol suite), and changes within a protocol layer are prevented from affecting the other layers. This greatly simplifies the task of designing and maintaining communication programs. Two examples of protocol suites are the OSI protocol suite, which has seven layers and includes every layer from the network application down to the hardware, and TCP/IP, which has two layers and is the foundation of network applications on the Internet.
Somewhere between the lowest protocol layer and the application, the data must be checked to be free of errors. Depending on the protocol suite, this error detection, and sometimes error correction, can be performed at one of a number of layers. In a paging environment, it is the data link layer that is responsible for both error detection and correction using a forward error correction (FEC) technique, well-known to people skilled in the art of paging and radio data protocols. Error detection and correction are vital for alphanumeric and binary data, but some types of data, such as voice data, may be designed to allow a certain amount of errors in transmission and therefore do not require FEC. Not only does FEC require significant processing, but FEC adds a data overhead of an additional 50% or more. Thus, FEC becomes a redundant procedure which results in a large required bandwidth and unnecessary processing in certain situations.
The present invention is directed to overcoming the foregoing and other disadvantages. More specifically, the present invention is directed to more efficient data transmission by selectively performing FEC on the data in the data link layer that requires FEC protection.